Over the years, various types of coin operated mechanisms such as parking meters, pay phones, photocopiers and vending machines have been developed to more effectively and efficiently provide automated services. These mechanisms usually accept the coins of the country in which they are located, however on occasion, other coins such as tokens might also be accepted by them. It has further been determined that it is not enough for a device to distinguish between the different coins from one country which are usually quite dissimilar, it is also necessary to be able to distinguish coins from several countries. In the latter case, coins are sometimes very similar physically, but not in denomination.
With the proliferation of coins around the world and the increased travel between countries, it is becoming more important to be able to distinguish coins from different countries and to distinguish between genuine coins, tokens and fake coins. Slugs and blanks can easily be made to resemble genuine domestic and foreign coins. Dependable coin identification requires sensitive and precise analysis.
Early coin operated devices were equipped to determine the denomination of a small number of coins. Typical prior art mechanisms served to discern the type and validity of the coin by means of various selectors of the mechanical or electro-mechanical type based on the geometric characteristics of the coins such as diameter, thickness, nature of the rim, whether smooth or knurled, the presence or absence of central bores, or on the basis of other physical characteristics of the coin such as weight. Such devices are generally not suitable to discard counterfeit coins particularly when the physical characteristics of the counterfeit coin are made to be close to those of a genuine coin.
More recent prior art devices utilize electronic sensors, rather than selectors of the mechanical or electromechanical type. The analysis of the coins is thereby performed on the basis of one or more electrical characteristics of the material or materials from which the coins are made, such as the magnetic permeability of the coins or their electrical conductivity, in addition to their physical characteristics.
Recently developed electronic devices are also more reliable and require less maintenance and servicing than the older type mechanical devices in that they have fewer if any moving parts.
Present day coin discriminating devices use a combination of electronic sensors to determine the signatures of a coin. As a typical example, U.S. Pat. No. 4,895,238 that issued to Speas on Jan. 23, 1990 describes a coin discriminator that has 4 sensors. The first sensor signals the presence of a coin. The second, a Hall-effect metal detector, senses the presence of any ferrous metal. The third sensor, an infrared LED/photo diode system, detects the coin diameter. The fourth sensor, a coil that causes the frequency of an oscillator to shift as a coin passes it, senses the metallic content of the coin. Thus two or more signatures of the coin are produced when the coin passes by the sensors. These signatures are compared with previously stored values and if the result of the comparison is within established limits the coin is identified and can be accepted. If the comparison result is outside the established limits, the coin can be rejected.
Further, as described in the above U.S. Patent, it is also common for the mechanism using the coin discriminator to have a main controller or microprocessor that receives signals from the sensors to control LCD displays and perform other functions such as detecting the presence of a vehicle through sonar and transmitting information to and from the mechanism through an infrared transceiver.
In order to simplify the sensing process, it has been found that the signatures for various coins can be obtained using only coils. U.S. Pat. No. 4,705,154 that issued to Masho et al on Nov. 10, 1987 describes a coin selection apparatus wherein two sets of coils are positioned along the path that a coin travels. The first set includes a pair of coils positioned on either side of the coin path and connected in series and in phase to establish flux lines across the path. The second set includes a pair of coils positioned on either side of the coin path and connected in series but in opposite phase to establish flux lines along the path. Both sets of coils are further connected in series to form part of a resonance circuit for an oscillator. As the coin passes the coils, the oscillator circuit detects a change in impedance in the coils and produces a change in the oscillator voltage output providing identifying signatures for the coin in question.
U.S. Pat. No. 5,244,070 that issued to Carmen et al on Sep. 14, 1993, also describes a dual coil coin sensing apparatus. In this particular apparatus, a pair of coils are placed along a coin path such that a coin will pass sequentially through the two coils which each establish flux lines along the path. The coils are connected in series as part of a resonance circuit in the feedback path of an oscillator circuit such that the frequency of the oscillator shifts as the coin passes by the coils. The shift in frequency provides identifying signatures for the coin which are compared to standard values stored in a table to determine the denomination of the coin if it is valid.
With the influx of coins from different countries as well as the ability to produce inexpensive counterfeits, it is more important then ever to be able to identify whether coins are genuine or not, and to identify their denomination.